CDSG, this is a question raised on another Forum that I am a member of. I'm sure that a member of this Group will have the answer, or directions on where to go to get it....
I can't attest to the accuracy of the statements in the question, just forwarding it as is...
Dennis

START:
" Does anyone know what happened to the massive projectile from the 800-mm (31") Gustav Gun / Dora?

I visited Bill Atwater at AP on two occasions with particular focus on the Gustav Gun and its projectile. It made the USN 16" shell look like a peashooter. For those not familiar with it the German Gustav Gun it was as long and heavy as a WW2 destroyer (155' long and 1,490 tons), had a crew of 250 to fire the gun and 2,500 men to lay the track and dig embankments.

The gun fired two types of projectiles using a 3000lb. charge of smokeless powder: a 10,584 lb. high explosive (HE) shell and a 16,540 lb. concrete-piercing projectile. By comparison USS Iowa's 16" High Capacity (HC) round weighed 1,900 lb and the APC (armor piercing), 2,700 lb.

Craters from Gustav's HE shells measured 30-ft. wide and 30-ft. deep while the concrete piercing projectile proved capable of penetrating 264-ft. of reinforced concrete before exploding! Maximum range was 23 miles with HE shells and 29 miles with concrete piercing projectiles. Muzzle velocity was approximately 2700 f.p.s.